Merge pull request micro-editor#3697 from JoeKar/doc/syntax

doc: syntax: Add hint about incompatibilities to previous versions

Author: JoeKar

runtime/syntax/README.md

@@ -6,11 +6,6 @@ Each yaml file specifies how to detect the filetype based on file extension or h
 In addition, a signature can be provided to help resolving ambiguities when multiple matching filetypes are detected.
 Then there are patterns and regions linked to highlight groups which tell micro how to highlight that filetype.
 
-Making your own syntax files is very simple. I recommend you check the file after you are finished with the
-[`syntax_checker.go`](./syntax_checker.go) program (located in this directory). Just place your yaml syntax
-file in the current directory and run `go run syntax_checker.go` and it will check every file. If there are no
-errors it will print `No issues!`.
-
 You can read more about how to write syntax files (and colorschemes) in the [colors](../help/colors.md) documentation.
 
 # Legacy '.micro' filetype
@@ -38,6 +33,19 @@ Micro syntax files are almost identical to Nano's, except for some key differenc
 * Micro does not use `icolor`. Instead, for a case insensitive match, use the case insensitive flag (`i`) in the regular expression
     * For example, `icolor green ".*"` would become `color green "(?i).*"`
 
+# Incompatibilities with older versions of micro
+
+With PR [#3458](https://github.com/zyedidia/micro/pull/3458) resp. commit
+[a9b513a](https://github.com/zyedidia/micro/commit/a9b513a28adaaa7782505dc1e284e1a0132cb66f)
+empty `rules: []` definitions are removed from all syntax files, since
+`rules` are no longer mandatory.
+Unfortunately they are mandatory for `micro` versions up to and including `v2.0.14`.
+
+To use newer syntax definitions from this repository with older `micro` versions
+you have to add these `rules: []` to all regions not including `rules` already.
+Otherwise you need to use syntax definitions before the above mentioned PR
+for example from version [v2.0.14](https://github.com/zyedidia/micro/tree/v2.0.14).
+
 # Using with colorschemes
 
 Not all of these files have been converted to use micro's colorscheme feature. Most of them just hardcode the colors, which can be problematic depending on the colorscheme you use.